In handheld work apparatus such as saw chains, blower/suction apparatus, brushcutters or the like having an internal combustion engine as a drive motor, a magnet wheel is attached to the crankshaft of the drive motor. The magnet wheel includes a magnet carrier of iron wherein at least one magnet is held by means of a magnet holder. The magnet wheel rotates during operation of the engine and the permanent magnet, which is held in the magnet wheel, is guided past an armature having a coil. The armature is fixed to the housing. A voltage is induced in the coil which is used to generate an ignition spark. The magnet carrier is made of iron and is geometrically so adapted that a suitable field-line course adjusts.
A low overall weight is required to facilitate carrying and guiding the work apparatus. The rotating masses should be kept as small as possible, especially for avoiding excessively large spinning forces or spinning torques. At the same time, a high mass moment of inertia of the movable parts is wanted for a quiet running of the engine. These parts act as a flywheel with which the non-uniformities of the running of the engine can be compensated especially in a single-cylinder configuration.
U.S. Pat. No. 5,477,841 discloses a magnetic ignition system of a portable handheld work apparatus wherein an annularly-shaped magnet carrier is mounted in a magnet wheel. Because of the annular shape of the magnet carrier made of iron, its mass lies at a large radius referred to the rotational axis whereby a high rotational moment of inertia results for a low overall weight. The magnet wheel configured in this way is formed of comparatively many individual parts and a separate hub is required.
U.S. Pat. No. 6,873,073 discloses a magnet wheel having a dumbbell-shaped magnet carrier. The magnet carrier is made up of a number of sheet metal pieces which are essentially configured to be identical and are stacked one atop the other to form a sheet metal packet. The sheet metal pieces each have a hub section whereby a hub is integrated into the sheet metal packet while omitting a separate component. In the arrangement shown, a comparatively high mass component is arranged close to the rotation axis which contributes only slightly to the rotational moment of inertia. The magnet wheel configured in this manner has a high inherent mass referred to the total mass moment of inertia.